The present invention relates to a filter and an image device with a filter.
Unwanted electromagnetic waves that electronic equipments produce may induce error operations in other electronic equipments so that their strict control within the limit of possibility is called for. In housings of electronic equipments, for example, these electromagnetic waves are restrained by means of interior metal plating or the like. On the other hand, for screens of image display devices such as CRTs (Cathode Ray Tubes), filters for the frontal surface are attached thereto with the purpose of suppressing the transmission of unwanted electromagnetic waves. Since such a filter for the frontal surface requires the transparency, layers composed of a fabric in mesh (referred to as a xe2x80x9cmeshxe2x80x9d hereinafter) with a conductivity, a transparent conductive film or such and a transparent substrate have been being utilized therein.
Further, in Japanese Patent Application Laid-open No. 211798/1991, there is disclosed an electromagnetic shielding plate that is two of transparent plates on which arrays of numerous conductive lines are fixed being put together.
In recent years, the plasma display panel (referred to as the xe2x80x9cPDPxe2x80x9d hereinafter) that is an image display equipment making use of the plasma discharge effect has been developed. The PDP, however, produces a large amount of unwanted electromagnetic radiation and, thus, what is required as a filter for its frontal surface is a filter having a strong suppression effect on the transmission of electromagnetic waves. Furthermore, in the PDP, the plasma discharge brings about the light radiation in the wavelength range of 850 to 1000 nm, which may cause an error operation in a remote control box for the PDP operations. Consequently, it is required that the filter for the frontal surface can also suppress the transmission of the light in this wavelength region. Further, since the PDP is a flat panel display with a large screen and, as the main body of the panel, a thin glass electrode substrate of a large size is employed, the filter for the frontal surface is also asked to fulfil the function of protecting that from the damage.
As a filter for the PDP frontal surface capable to serve all these functions, there is in use, for instance, a filter disclosed in Japanese Patent Application Laid-open No. 247583/1997, wherein a conductive mesh made of polyester filaments which are covered, in succession, with copper and nickel is laid on a transparent resin sheet that is provided with a function of absorbing the light in the near infrared region.
In order to show bright images even when a filter is placed in front of an image device, it is essential to enhance the transmittance of the filter for the light beam. Nevertheless, when the diameter of filaments or the like which constitute the mesh in the filter is set thin and besides the pitch of the mesh is set wide, for the sake of increasing the transmittance of the filter for the light beam, a dispersion in spacing of the mesh becomes large, making the appearance poor. In effect, it is difficult to manufacture a mesh whose aperture ratio that is a ratio of the transparent section per unit area is not less than 70%, and a filter with a high transmittance for the light beam has not been obtained yet.
Moreover, mutual interference between two types of line groups, which are a group of borderlines between pixels and a group of lines constituting the mesh, brings about the moire. For a method to make the moire inconspicuous, there is first considered a method wherein the line diameter is made thinner and thereby the moire is made inconspicuous, but the fabrication of a mesh with a thin line diameter is difficult, due to the above reasons. Another method therefor is a method wherein the pitch of the mesh is set to be a pitch where the moire becomes inconspicuous. Meanwhile, the mesh is, in general, plain weave, having lines which intersect at right angles and equal pitches in two directions. In contrast with this, lengths of a pixel of an image device in the vertical direction and in the horizontal direction are not generally equal. Therefore, when a mesh is placed in front of an image device, there are certain cases in which, while the moire resulting from the mutual interference between the group of borderlines of pixels in the vertical direction and the group of lines of the mesh in the vertical direction is inconspicuous, the moire caused by the mutual interference between the group of borderlines of pixels in the horizontal direction and the group of lines of the mesh in the horizontal direction is conspicuous. Conversely, in some cases, although the moire resulting from the mutual interference between line groups in the horizontal direction is inconspicuous, the moire caused by the mutual interference between line groups in the vertical direction is conspicuous. In order to make the moire inconspicuous, there is, in addition, another method wherein the lines of the mesh are arranged to make angles of, for example, 45 degrees or so with respect to the borderlines of pixels.
However, when these angles are to be set at or above 20 degrees, in other words, when the crossing angles between borderlines of pixels and lines of the mesh are to be set at or above 20 degrees, in fabricating a filter, a large amount of end sections of the mesh must be cut and removed so that a problem of high production cost for the filter arises.
Further, in Japanese Patent Application Laid-open No.211798/1991, with regard to techniques of the moire prevention, nothing is disclosed or suggested.
An object of the present invention is to provide a filter which has a higher aperture ratio than the one utilizing a conventional conductive mesh made of polyester filaments which are covered, in succession, with copper and nickel. Another object of the present invention is to provide, by disposing this filter in front of an image device with rectangular pixels, an image device of high quality without any conspicuous moire.
The present invention relates to a transparent filter comprising a sheet-shaped body and numerous linear conductive elements arrayed on a surface thereof, which is adapted to be disposed in front of an image device having rectangular pixels; wherein the conductive elements with a linewidth of 50 xcexcm or less are arrayed on the sheet-shaped body in two directions with a pitch P1 and a pitch P2, respectively; an aperture ratio of the filter is not less than 70%; and when lengths of a pixel of the image device in vertical direction Y and in horizontal direction X are denoted by W1 and W2, respectively, P1, P2, W1 and W2 satisfy one of relations expressed by following equations, that is, both Equation (1) and Equation (2), both Equation (3) and Equation (4), both Equation (5) and Equation (6), or both Equation (7) and Equation (8),
n1+0.35xe2x89xa6W1/P1xe2x89xa6n1+0.65xe2x80x83xe2x80x83(1)
n2+0.35xe2x89xa6W2/P2xe2x89xa6n2+0.65xe2x80x83xe2x80x83(2)
n1+0.35xe2x89xa6P1/W1xe2x89xa6n1+0.65xe2x80x83xe2x80x83(3)
xe2x80x83n2+0.35xe2x89xa6P2/W2xe2x89xa6n2+0.65xe2x80x83xe2x80x83(4)
n1+0.35xe2x89xa6W1/P2xe2x89xa6n1+0.65xe2x80x83xe2x80x83(5)
n2+0.35xe2x89xa6W2/P1xe2x89xa6n2+0.65xe2x80x83xe2x80x83(6)
n1+0.35xe2x89xa6P1/W2xe2x89xa6n1+0.65xe2x80x83xe2x80x83(7)
n2+0.35xe2x89xa6P2/W1xe2x89xa6n2+0.65xe2x80x83xe2x80x83(8)
(Each of n1 and n2 is an integer from 1 to 5).
When this filter is disposed in front of an image device, it can be disposed in such a way that narrower angles xcex81 and xcex82 between angles which are formed by the directions of the lengths for the linear conductive elements of the filter with the vertical direction Y and the horizontal direction X of the image device, respectively, cannot be such large angles as a conventional angle of 45 degrees or so, but can be, in both cases, within a range of small angles of 18 degrees or less.